Sharpening stone



FIG. 1 is an isometric view of the sharpening stone showing our new design;

FIG. 2 is a front view thereof, with the rear view being identical but reversed;

FIG. 3 is a right side view thereof, with the left side being identical;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof. 

The ornamental design for a sharpening stone, as shown and described. 